1. Field of the Invention
The present invention relates to a heating cartridge for a thermostatic element, as well as a method for manufacturing such a cartridge. It also relates to a thermostatic valve including such a cartridge.
2. Brief Description of the Related Art
In many applications of the fluidics field, in particular for cooling of thermal engines of vehicles, thermostatic valves are used to distribute a fluid entering into different circulation channels, depending on the temperature of that fluid. These valves are called thermostatic in the sense that the movement of their internal plug(s) is controlled by a thermostatic element, i.e. an element which comprises a cup containing a thermo-expandable substance and a piston which is slidingly displaceable with respect to the cup under the action of the thermo-expandable substance during the expansion thereof.
In order to distribute the fluid depending on other parameters, in particular conditions outside the valve such as the ambient temperature or the load of the vehicle propelled by the engine equipped with the valve, it is known to integrate an electric cartridge into the valve to heat the thermo-expandable substance, which makes it possible to steer the valve from the outside thereof, independently or as a complement to the temperature of the entering fluid, in particular using a computer onboard the vehicle and programmed appropriately. In practice, the heating cartridge comprises electric heating means, such as a heating resistor, arranged inside the aforementioned piston or a similar tube: by immobilizing, for example, the piston at the external case of the valve, the electrical supply of the resistor causes an increase in temperature of the thermo-expandable substance, which causes, through expansion of the latter part, the sliding of the cup around the piston, a plug being supported by said cup to act on the circulation of the fluid through the valve.
In order to electrically supply the heating means, the cartridge comprises connectors to electrically connect electric conduction wires, belonging to the heating means, and charge ports connected to an external current source. These connectors are supported by a base integral with the tube, this base thus undergoing, at least in part, the strains absorbed by the piston during use.
In this context, DE-A-103 03 133 proposed to strengthen the mechanical resistance of the connection between the base and the tube, by realizing the base through molding of a plastic substance injected on either side of a flat clamping plate, provided at the end of the tube in a radial plane at said tube end. This radical solution has proven difficult to carry out in practice, inasmuch as it requires having injection molds adapted, simultaneously, to each possible shape and size for the tube and the total axial dimension that one wishes to obtain for the heating cartridge. The molding cost to meet the different geometries of heating cartridges therefore becomes crippling.